Recent trends have provided receivers that support not just conventional one-way communication from the signal head end to the receiver, but also two-way communication, to support so-called “interactive digital video”, Examples of interactive digital video include pay-per-view, in which a receiver user can input certain requests and commands, as well as purchase orders, for pay-per-view programming using the receiver, and video-on-demand, entailing many of the same communication considerations. Also, so-called “switched digital” can be implemented using two-way receivers. Switched digital in essence allows all the viewers in a particular area to in essence report back to the head end what channel they are viewing, so that, for instance, the head end may take intelligent steps with respect to bandwidth such as ceasing transmission into the area of a channel that is not currently being viewed by anyone in the area and thereby releasing bandwidth for other uses.
Partly to support such two-way interactive digital video, the Open Cable Application Platform (OCAP) has been introduced. In effect, OCAP defines an application platform's basic functionality and standardizes on an API (application program interface). The basic functionality allows applications to be detected on the signal and download dynamically from the signal head-end. The API implemented by the receiver platform allows these downloaded software applications, to execute and communicate with the receiver through a common standard interface to manage the receiver's resources and exploit its functionality. An OCAP interface also allows the application to communicate through the receiver's communication port with the TV signal head end and with the home network. In this way, for example, viewer purchases of video-on-demand may be facilitated through a downloaded VOD application, with the purchased video then transmitted from the head end to the receiver, to be decrypted by the cable card of the receiver and then rendered through the display output.
When multiple users in a same household want to interact with the service simultaneously and independently of each other the industry has chosen the simple path of supporting the execution one instance of the application per user by provisioning a complete OCAP environment per user, requiring the replication of a complete receiver's hardware and middleware per user. Although this approach is very expensive it has the benefit of being very simple in that the OCAP application instances can always rely on all the cable resources of the receiver be available to them at all times and hence don't have to cope with the burden of sharing resources with another instance as each instance executes in its independent OCAP environment.